Although US Defense Secretary Leon Panetta and his Israeli counterpart, Ehud
Barak, still disagree on the utility of continued sanctions, both now accept a
more ominous understanding. The cumulative effect of sanctions designed to slow
Iranian nuclearization has not worked thus far. Almost certainly, both
acknowledge, and within a year, unless it is stopped at the 11th hour by
substantially more immediate and tangible military measures, Tehran will enter
the “Nuclear Club.”

What happens next? Whether attempted by the US or
Israel, or both together, exercising a successful preemption option at this 11th
hour would be numbingly problematic. At the same time, rejecting this military
option altogether, on operational grounds, could expose Israel to intolerable
conditions of extended vulnerability.

In essence, foregoing anticipatory
self-defense, the legal equivalent of a permissible first-strike, could mean
that Israel will have to live under the unending threat of a nuclear sword of
Damocles. Even worse, unless it can be assumed that Iran’s leadership will
remain consistently rational, thus always valuing national survival more highly
than any other preference, or combination of preferences, there might remain few
if any viable prospects for Israeli nuclear deterrence.

In such dire –
but altogether conceivable circumstances – Israel’s only still-available
foundation for physical survival might even be its active defenses.

What
would this mean? The core of Israel’s active defense plan for Iran remains the
Arrow anti-ballistic missile program. Iron Dome, a corollary and interrelated
system, is intended primarily for intercepting shorter-range rocket attacks. At
first glance, looked at exclusively from Israel’s technical side, everything may
appear promising. In principle, at least, the implications of Israel’s no longer
viable preemption option could remain tolerable.

Still, upon closer
reflection, a grave problem emerges.

THIS DIFFICULTY lies in making
untenable assumptions about any system of active defense. In short, in a world
of multiple enemies, no system of ballistic missile defense, even the IAF’s
newly upgraded interceptors known as “Block 4,” can ever be reliable enough to
preclude an associated strategy of deterrence. Reliability of intercept is a
“soft” concept. In reality, any missile-defense system will always have some
“leakage.” Panetta and Barak are both well aware of this critical
limitation.

A small number of Iranian missiles penetrating Arrow and
related defenses might be “acceptable” if their warheads contained “only”
conventional high explosives, or chemical high explosives. But if the
incoming warheads were in any measure nuclear and/or biological, even an
extremely low rate of leakage would be unacceptable.

In the next few
months, Israel must move, recognizably, to strengthen its still-ambiguous
nuclear-deterrence posture. To be dissuaded from launching an attack, a rational
adversary would always need to calculate that Israel’s second-strike forces were
sufficiently invulnerable to any contemplated first-strike
aggressions.

Facing Israel’s Arrow, this adversary could require steadily
increasing numbers of missiles in order to achieve an assuredly destructive
first-strike capability. Still, once Iran was able to assemble a certain
determinably larger number of deliverable nuclear warheads, Arrow could cease to
serve the indispensable and lesser known deterrence function of its security
mission.

ISRAEL MUST continue to develop, test and implement an
interception capability to match the cumulative enemy threat. Simultaneously, it
must also take considered steps to enhance the credibility of its still-opaque
nuclear deterrent.

More precisely, if Iranian nuclearization proceeds
unhindered, Israel should prepare to take its bomb out of the “basement” on very
short notice, thus ending Jerusalem’s tacit nuclear policy of “deliberate
ambiguity.” Israel, of course, has already operationalized a robust
second-strike nuclear force. This force, hardened and dispersed, must now also
be made more recognizably ready to inflict an unacceptable retaliatory salvo. As
purely “counterforce” targeting could have inadequate deterrence benefits,
Israel’s nuclear targets must be identifiable enemy cities. Soon, it may also be
the optimal time to remind Iran of Israel’s expanding deployment of certain
sea-based deterrent forces.

Always, Israel must clarify that Arrow and
other defenses would operate simultaneously, or in tandem, with Israeli nuclear
retaliations. Iran must be made to understand that Israel’s defensive
deployments would never preclude, or render less probable, an Israeli nuclear
reprisal.

In the best circumstances, Iran would never have been allowed
to proceed toward full military nuclearization with impunity. Now, however,
Israel will have to deal with a persistently recalcitrant enemy regime by
implementing steady enhancements of its nuclear deterrence and active defense
capabilities.

Although a regime-change in Tehran might first appear to be
an attractive alternative option, any such transformation might offer Israel
only temporary national-security benefits. Moreover, it is not out of the
question that a successor regime in Tehran could prove even worse for Israel,
and for the US.

Iranian nuclear harms could be directed toward Israel,
not only via direct-missile strikes, but also by terrorist- proxy delivery
systems, including cars, trucks and boats. Should a newly-nuclear Iran ever
decide to share its weapons-usable materials and scientific personnel with
Hezbollah in Lebanon, for example, Israel might also have to face a heightened
prospect of nuclear terrorism. The considerable dangers posed could impact
American cities as well.

Today, whatever their continuing disagreement on
further sanctions, Panetta, Barak, and their respective heads of state, must
make an unenviable operational decision. More than likely, in their prudent
cost-benefit calculations, the preemption option will have to be rejected. Other
plans will have to be made for dealing with a soon-to-be nuclear
Iran.

Successfully deterring a possibly irrational nuclear adversary in
Tehran is not out of the question.

After all, such an adversary might
still have a consistent hierarchy of preferences. Directed by this sort of
hierarchy, Iran’s decision-makers could reasonably calculate that the benefits
of any long-term peace with Israel are actually greater than the expected
benefits of war.

The task for Israel and the United States will then be
to correctly identify: (1) Iran’s very highest preferences (almost certain to be
religion-based); and (2) credible ways to most convincingly and substantially
threaten these core Iranian values.

This task is formidable, but it can
be accomplished.

Louis René Beres is Professor of Political Science and
International Law at Purdue. General John T. Chain was commander-in-chief, US
Strategic Air Command, and director, Joint Strategic Target Planning Staff.

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